It is common practice in automotive climate control to determine the thermal comfort level of a passenger compartment by drawing a stream of air from the compartment across a sensor to measure the air temperature and to estimate the effect of sun load on the occupants by a solar sensor mounted on top of the instrument panel for exposure to the sun. These measurements are combined with measurements of outside air temperature and engine coolant temperature and an operator selected comfort setting to supply a control algorithm with the data needed to determine the optimum settings for HVAC mode, blower speed, and mix door settings which together determine outlet air temperature and air speed needed to achieve the comfort setting.
It has been proposed to replace solar sensing or both solar sensing and inside air temperature measurement with infrared (IR) sensing which directly detects the temperature of the occupant seating area and the occupants themselves. Thus irradiation from seat surfaces, occupant skin and occupant clothing, as well as any object in view of an IR sensor becomes a prime control parameter. The IR sensor includes a thermopile in a protective envelope having a window for viewing the desired portion of the vehicle interior, so that the thermopile can sense the temperature of the viewed region. The IR sensor is subject to change in efficiency due to accumulation of dirt or other matter on the window, so that its output or the weight given to the output should be adjusted to compensate for such changes.